An advanced ion chromatographic technique was first reported in 1975 by Small, H., Steven, T. S., and Bauman, W. C., Anal. Chem. 47, 1801 (1975). It was performed in a system consisting of two ion exchange columns connected in series followed by an electrical conductivity detector. A sample was delivered by a stream of flowing eluent to the first ion exchange column. In passing through the column, ions were separated into discrete bands based upon their relative affinity for functional groups on the surface of a pellicular ion exchange resin packed into the column. These discrete bands of ions appearing in effluent from the first (separator) column are thus available for detection, identification and quantitation.
Using only the separator columns, such as those available to Small et al., it is difficult, however, to detect the separated ions at low concentrations because of a poor signal to noise ratio obtainable in the electrical conductivity detector. Because of this, the effluent from the separator column was passed through a second (suppressor) ion exchange column which contained a packing having functional groups of opposite charge to those on the resin in the separator column. The suppressor column functioned to enhance the conductivity signal of the separated bands of ions and simultaneously minimize the background conductivity signal from the eluent.
A new and improved method of ion chromatography utilizing only the separating column of optimized ion exchange capacity connected directly to a conductivity detector was reported in 1979 by Fritz and coworkers. See D. T. Gjerde, J. S. Fritz, and G. Schmuckler, J. Chromatogr. 186 (1979) 509; and D. T. Gjerde, G. Schmuckler, and J. S. Fritz, J. Chromatogr. 187 (1980) 35.
Since the advent of modern ion chromatography, additional techniques and apparatus have been developed to expand its utility to a wider range of ions. For example, the need to quantitate low concentrations of weakly ionized organic acids led to the development of an ion chromatographic separation based upon the principle of ion exclusion. Rich, W., Smith, F., Jr., McNeil, L. and Sidebottom, T., "Ion Exclusion Coupled to Ion Chromatography: Instrumentation an Application", Ion Chromatographic Analysis of Environmental Pollutants(Ann Arbor Science, Ann Arbor, Mich. 1979), vol. 2, p. 17. Moreover, high performance columns, detectors and other hardware have been developed. For example, amperometric and optical detectors have been employed in addition to the classical conductivity detectors. Additionally, suppressor columns and chemistries have been improved.
Despite the rapid development of methods and apparatus, there are still some situations in which it is inconvenient and time consuming to employ ion chromatography for the required analyses. One such instance occurs in the nuclear power industry. If, for example, a pressurized water reactor accident occurs, boric acid, a neutron absorber, is released into the reactor water to control the fissioning process. It is imperative in such accidents to closely monitor borate levels to ensure that the reactor shuts down. Typically, calibration curves and sample analysis for borate must be accomplished in about 2.5 hours. After about 96 hours from the start of such an accident, it is also necessary to analyze the reactor water for additional anions, particularly chloride.
The current technique for chloride analysis in the nuclear power industry employs an on-line ion chromatograph containing pellicular anion exchange resin, a chemical suppression system and a conductivity detector. Borate analysis is accomplished manually using a laboratory ion chromatograph with chemical suppression and a conductivity detector. Samples employed for borate analysis must be diluted prior to injection into the column and total analysis time per sample is around 20 minutes.
Since borate analysis is a partially manual operation, technicians risk exposure to highly radioactive samples. In addition, the run time per sample for borate is considerably longer than desired.
Because of these difficulties, borate analysis is still performed in many cases by titrimetric techniques.